Integrated circuit ("IC") chips are steadily becoming smaller and more powerful. When compared to previous integrated circuit chips, this trend produces integrated circuit chips which are significantly more dense and which perform many more functions in a given period of time. This results in an increase in the electric current used by these integrated circuit chips. Consequently, smaller and more powerful integrated circuit chips tend to generate significantly more heat than larger and less powerful IC chips. Accordingly, heat management in electronic products has become a chief concern in IC chip design.
Reliability of electronic circuits is dependent upon proper matches in the coefficients of thermal expansion of various electronic components. For example, as temperature rises, mismatches in the coefficients of thermal expansion cause stresses to develop between electronic components. Under these circumstances, any increase in operating temperature will have a negative effect on reliability. In an effort to control heat better, the use of various heat sinks is now a central focus in electronic equipment design. Examples of common heat sinks employed today include: IBM Thermal Conductive Modules (ITCM); Mitsubishi High Thermal Conduction Modules (HTCM); Hitachi SiC Heat Sinks; Fujitsu FACOM VP2000 Cooling Mechanisms; or metal plates of copper or aluminum, for example.
In order to mate IC chips to heat sinks successfully, an interface which is elastic or otherwise conformable is preferred so as to ease installation and to minimize the effect of expansion and contraction between electronic components. Air gaps formed from improper installation of a chip to a heat sink, or expansion and contraction cycles during operation, can greatly impede the flow of heat from an IC chip. Conformability becomes especially important when the tolerances on the heat sink and chip tilt (in the case of flip chips) become large.
To date, thermal greases have been known to be a preferred material for use as an interface between heat sinks and electronic devices. While thermal greases may operate with success in such applications, they are replete with shortcomings which detract from their usefulness. For example, thermal greases tend to be difficult to control and are prone to contaminating components of an electronic device. Care must be taken when using these materials to prevent unwanted contamination of solder joints, and in the case of electrically conductive thermoset resins, unwanted contamination of adjacent conductors. In practice, this usually results in a significant amount of wasted material. Additionally, clean up of such materials often requires the use of solvents.
In U.S. Pat. No. 5,187,283, a gasket-type material is disclosed comprising a thin-film surrounding a meltable metal core. In operation, the gasket is installed as an interface and its temperature is increased to melt the metal core, which allows it to conform to the component parts. Unfortunately, this construction is believed to be ineffective in avoiding air gaps that can form during normal thermal cycling of the device. Further, as is a common problem with solid gasket materials in general, it is believed that this device may experience limited compressibility, requiring either the application of excessive pressure to the mating surfaces, or the use of unacceptably thick sections of the gasket.
U.S. Pat. No. 5,060,114, teaches that conformability may be obtained by curing a metal or metal oxide filled silicone around the component to be cooled. Although this method may be successful, it is believed to be unduly complicated, costly, and time consuming for practical widespread use.
Most commercially available products produce a conductivity of about 0.7 W/M .degree.C. (for greases) to about 1.4 W/M .degree.C. (for epoxies). Even the most advanced (and expensive) materials, such as silver filled epoxies, only achieve a conductivity in the range of about 3 to 4 W/M .degree.C. With regard to easily handled materials, such as self-adhesive materials, these materials can typically achieve a conductivity of only about 0.37 to about 1.5 W/M .degree.C., respectively. Although these commercial materials can produce better conductivities at high mounting pressures, they deliver extremely poor conductivity at very low mounting pressures (e.g., pressures below 10 lbs/in.sup.2).
The foregoing illustrates limitations which exist in known thermally conductive articles. Thus, it is apparent that it would be advantageous to provide an improved thermally conductive article directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.